Moulded back-up pad



Dec. 26, 1961 D. J. OLTON 3,014,319

MOULDED BACK-UP PAD Filed July 20, 1960 FIG .4

INVENTOR DIRCK J. OLTON ATTORNEY United States Patent Ofiice PatentedDec. 26, 1961 The present invention relates in general to supportingdevices for coated abrasive discs and more particularly to a resilientback-up pad having improved wear and other operating characteristics.

It has heretofore been proposed to utilize back-up pads for supportingdevices for coated abrasive discs wherein the surface of the pad incontact with the uncoated side of the abrasive disc is resilient innature, i.e., is formed of foam rubber or the like. Such soft-surfacedpads have generally had a relatively short wear life due to the tendencyof the material to tear and therefore a common practice is to interposea canvas face between the soft pad material and the abrasive disc to bemounted thereon. The resulting combination has found wide-spread usage111 industry but is still subject to poor life, snagging, etc. Animproved pad of this type is described and claimed in my copendingapplication, Serial No. 29,985, filed May 18, 1960, and the presentinvention represents a still further improvement in pads of this kind.

Accordingly, it is an object of the present invention to provide animproved coated abrasive back-up pad.

Another object of the invention is to provide an improved workingsurface for a resilient coated abrasive back-up pad.

A' further object is to provide a coated abrasive backup pad capable ofeasy replacement and possessing improved ability to be driven by themachine upon which it is mounted.

Additional objects if not specifically, set forth herein will be readilyapparent to one skilled in the art from the following detaileddescription of the invention.

In the drawings: I

FIGURE 1 is a top plan view of a coated abrasive back-up pad of thepresent invention.

FIGURE 2 is a bottom plan View of a replacement pad of the presentinvention.

FIGURE 3 is a side elevation of the pads illustrated in FIGURES 1 and 2.

FIGURE 4 is a side elevation of a modification of a pad incorporatingthe present invention.

Generally, as described and claimed in my aforesaid application, SerialNo. 29,985, the present invention contemplates a back-up pad for coatedabrasive discs wherein the body of the pad is made up chiefly of a toughcellular, resilient material such as polyurethane foam. Foam rubber orother materials of a like nature may be used and will form an improvedproduct when the features of the present invention are incorporated intopads made therewith, but preferably the material utilized for the bodyof the pad is polyurethane foam. This material is tougher and moretear-resistant than foam rubber for example.

Specifically, the tough cellular resilient material is recessed at itsworking surface to receive a planar canvas insert. The canvas or similarmaterial must be substantially flush with the non-recessed'portions ofthe working surface of the cellular, resilient material. Preferably thisstructure is achieved by placing the canvas insert into the base of themold used in theformation of the cellular main portion of the back-uppad. The material to be used is poured into the mold over the canvasdisc, foamed in situ and the composite structure removed from the mold.This construction produces a pad having many advantages including thatof not marring the workpiece to applied. The rim of cellular materialaround the periphery of the pad protects the work from the edge of therelatively stiif canvas and prevents snagging or scoring of the work.Also, by being recessed the canvas insert will resist to a marked degreeany separation from the cellular. back-up material. Tests indicate alife of two or three times that of a similar pad having the canvas facesecured in non-recessed fashion to the cellular material.

A further innovation has been utilized to permit easy replacement of thecellular, resilient portion of the pad. Heretofore such portions havegenerally been held to the stiff, hard rubber back-up plate member bymeans of an adhesive. Replacement elements have been glued on or havebeen furnished with a stiff plastic or rubber plate glued to the base ofthe cellular member with a center hole adapted to permit the assembly tobe held to the hard rubber back-up plate with a threaded shaft. In thecase of the direct adhesive attachment of the cellular body to theback-up member, the disadvantages are obvious-cleaning the old adhesiveand remnants of the old pad preparatory to applying the new pad to thesupporting surface make this impractical. With a plastic face applied tothe base of the cellular member, difficulty in preventing slippage ofthe plastic upon the face of the back-up member occurs. This can becorrected by tightening the threaded shaft to an extreme degree, butsuch measures result in early destruction of the cellular body throughshearing between the body and the plastic at the interface between thetwo. The problem was to some extent overcome in the case of theinvention described and claimed in Serial No. 29,985 by again recessingthe base of the cellular body to receive the stiffening insert. Theinsert of plastic, hard rubber, thin steel, or the like, 'waspreferablyapplied byinsertion into the foamed cellular material while in the mold.With a rim of cellular material left flush with the surface of theperiphery of the insert, the device when placed upon the driving backupplate had substantially no slippage.

-However, I have now found that still further improvement is possible byextending the cellular material beyond the plane of the insert member,i.e. either forming a a raised rim around the periphery of the insertmember or extending the cellular material at least partially over thesurface of such insert member. I

Referring now to the drawings, FIGURE 1 illustrates the pad 10 of thepresent invention in top plan view,

which the pad and its associated coated abrasive disc is showingthecanvas insert 11 and therim of cellular, resilient material 12surrounding insert 11. 7

FIGURE 2 illustrates the base of a cellular pad 20 adapted for use as areplacement pad to be used with a permanent, recessed center hard rubberback-up plate. The outer periphery of the working surface is shown at21. This would correspond to the outer periphery of the rim 12 shown inFIGURE 1. The outer periphery at the base of the cellular member 20 isshown at 22. The plastic insert is shown at 23 with a raised centerportion 24 and center hole (threaded) 25 adapted to conform to thepermanent back-up plate (not shown). The area defined by lines 22 and 26is the raised rim of cellular material referred to above.

FIGURE 3 illustrates in detail a side view of the pad of FIGURES 1 and2. The body of cellular resilient material is shown at 30 with thecanvas insert illustrated in dotted lines at 31. The plastic face orinsert in the base is identified by reference numeral 32, showing theraised central portion 33 and threaded center hole 34. The raised rim ofcellular material at the base of the pad is identified by referencenumeral 35.

FIGURE 4 shows a side view of a pad similar to that of FIGURES 1 and 2except that the cellular material, instead of extending in rim formbeyond the plane of the base insert, actually covers a portion of suchinsert. The

cellular body of the pad is shown at 40 with the canvas insert in theface at 41. The plastic or other relatively rigid base insert is shownat 42 with the raised central portion 43 and threaded center hole 44.The portion of cellular material extending beyond the plane of insert 42and over the outer face thereof is shown at 45. This layer may be quitethin and preferably should not exceed about A1" in thickness.

In both modifications described above, the extension of the cellularmaterial beyond the plane of the base insert provides a much firmernon-skid bond between the pad and the drive pad to which it is affixedin use than Where the cellular material is flush with the insert asdescribed and claimed in my aforesaid earlier application. In the caseof the rim, as illustrated most clearly in FIG- URE 3, pressure on theouter face of the plastic insert will cause such rim to fold over theedge of the insert and grip the same for improved drive. In the case ofthe actual coverage of the insert as shown in FIGURE 4, the frictionalcontact between the face of the driving pad (not shown) and the base ofthe back-up pad is substantially increased due to the nature of thecellular material.

be of a woven or non-woven nature, preferably canvas,

capable of providing an adhesive-receiving surface to which coatedabrasive discs may be held adhesively and then stripped therefromwithout marked deterioration of such surface. Frequently, pads of thistype are used with open mesh abrasive products and in such instancesadhesive is not required to hold the disc to the pad. The insert must becapable, however, of resisting the abrading action of such a disc to agreater degree than the cellular material. The top insert may thereforebe described as a material of higher internal strength than the cellularmaterial in which it is embedded. Likewise, the base insert, which isused for replaceable pads, may be made of any suitable material such asfabric, steel, plastic, etc. Again, it must be of higher internalstrength than the cellular material in which it is embedded andpreferably is substantially rigid in nature as compared to the cellularmaterial. The cellular material should be tough and resilient and thebody formed thereof should be relatively thick compared to the thicknessof the inserts. A typical commercial pad uses a thickness of cellularmaterial of 1%" with a plastic insert of A thickness and a canvas insertof thickness. Approximately A" of cellular material should be leftaround the periphery of each insert for best results.

The term substantially planar as used in the appended claims is intendedto cover both planar inserts 4 and inserts having a raised or depressedcenterportion such as is illustrated at 33 in FIGURE 3 and at 43 inFIGURE 4 of the drawingshereof.

I claim:

l. A back-up pad for use with a coated abrasive disc characterized by arelatively thick body portion of tough, resilient, cellular materialhaving a relatively stiff, thin, substantially planar insert of amaterial having a higher internal strength than said cellular materialembedded in the lower face of said body portion, said cellular materialextending outwardly at least partially beyond the planar surface of saidinsert.

2. A pad as in claim 1 wherein the body portion has a fabric insert inthe upper face thereof adapted to support the coated abrasive disc.

3. A back-up pad for use with a coated abrasive disc comprising: arelatively thick body portion of tough, resilient, cellular materialhaving a circular upper face and a circular lower face; a relativelythin circular canvas insert of lesser diameter than said circular upperface embedded in such face with the outer surface of said insertsubstantially fiush with the upper surface of the periphery of suchface; and a relatively thin, rigid circular insert member of lesserdiameter than said circular lower face embedded in such face with thecellular material of such face extending outwardly at least partiallybeyond the plane of said rigid insert.

4. A back-up pad for use with a coated abrasive disc comprising arelatively thick body portion of a tough, resilient, cellular materialhaving circular upper and lower faces; a canvas insert moulded flushinto said upper face and a second insert of more rigid material mouldedinto said lower face so that each of said inserts is surrounded by a rimof said tough, resilient cellular material; said lower rim of tough,resilient cellular material extending outwardly beyond the plane of theouter surface of said References Cited in the file of this patent UNITEDSTATES PATENTS Newcomb June 16, 1931 Welch Aug. 30, 1960

